Hello,
I am trying to set up an SMTP mail relay on my Debian server using OpenSMTPD. I was following this SMTP setup tutorial and it seemed to be going smoothly, but I keep running into an issue when I keep sending an email.
Here is the command I’m using to send a test email:
echo "Test email body" | mail --subject="Test Subject" --append="From: monitoring@example.com" myemail@example.com
But I get an error message:
mail: cannot send message: Process exited with a non-zero status
I checked the logs using journalctl -f _COMM=smtpd, but I can’t figure out what’s wrong. The logs show:
Invalid recipient: <myemail@example.com>
Does anyone know what could be wrong here?
I changed the email names and such for privacy reasons.
Ok, so my first recommendation would “use Postfix”.
If you “apt install postfix” on a Debian system it will work right out of the box.
When you find that you can’t actually relay directly anymore and that you need to
chain on to an external service like “Mailjet” (or similar), you will be glad that the code to do this is available and well documented. (and typically “just works”)
If you take apart many of the “well known” systems that utilise SMTP servers (“maininabox” for example) , you will find that under the hood, many are using postfix.
In terms of pedigree, I believe “postfix” was originally contributed by “IBM”.
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Followup; having subsequently had occasion to play with OpenSMTPd in some detail, I’m still of the opinion that generally you’re far better off with Postfix. That said (!) if you want a really lightweight solution and are prepared for a maybe less well documented / supported approach, OpenSMTPd does work.
For my configuration, I have a config file in /etc/smtpd.conf that goes like this;
listen on localhost
table aliases file:/etc/aliases
action "local" mbox alias <aliases>
action "relay" relay host smtp://email.madpenguin.uk
match from local for local action "local"
match from local for any action "relay"
So to break this down a little;
- listen controls which address and port the server listens on, so in this instance we’re only listening for local connections on the default port number which will be 25
- table sets up a reference to our standard system aliases table, which takes the form; user: alias … so for example you could put in; root: myname@gmail.com and all email to the local root user would be forwarded to the designated gmail account.
- action is used to set up the desired actions, in this instance “local” will deliver to the local system using the “aliases” table, and “relay” will relay messages to the specified smtp server.
- match is where all the good stuff happens. “from local” limits the routing of emails to those originating on this server. “for local” routes emails to local addresses via our “local” action. “for any” routes any remaining emails via our “relay” action.
In your example, my guess would be that your error comes about because you’ve specified a non-local email address (@example.com) without setting up a “for any” action, OR, of you have example.com as your local domain, “myemail” is not a local user and not present in the aliases table.